MFC r330558:

[ig4] Add support for i2c controllers on Skylake and Kaby Lake

This was tested by Ben on HP Chromebook 13 G1 with a
Skylake CPU and Sunrise Point-LP I2C controller and by me on
Minnowboard Turbot with Atom E3826 (formerly Bay Trail)

Submitted by: Ben Pye <ben@curlybracket.co.uk>
Reviewed by: gonzo
Obtained from: DragonflyBSD (a4549657 by Imre Vadász)
Differential Revision: https://reviews.freebsd.org/D13654